[platz]

The bulk of real Haskell programs do not choose such granular restriction of side-effects that it's unmaintainable. As always, there are tradeoffs. In most applications, the code at application boundaries live in some Monad that are based on IO.

For Example, Yesod gives you the Handler monad, which is based in IO, and really just exists to provide access to runtime/request information, so at the API handler level you can do anything you need to. But what's nice is that not everything has to live in IO, and so in places where it makes sense, such as a parser, we can say that parser doesn't need IO, because that wouldn't make sense.

And my point here is that just having the ability to separate between IO and non-IO is very useful; we also do not have to split every single effect down into it's own special, separate type; in many cases that would just be overkill.